Online Time Killer: Pandemic 2

Here's a fun game called Pandemic II that lets you create an infectious disease and try to wipe out Earth's human population. You get to name your disease and then select whether it is a virus, bacteria or parasite. As the game goes on you try to evolve your disease to make it more and more deadly. Breaking news items tell you about your progress and other events happening in the world. You can use your evolution points to strengthen your disease. If you start to do well scientists will try to come up with vaccines to stop you.

You should watch the tutorial as the game is a more complex than typical arcade and shoot-em up games.